Post-menopausal women will be given estrogen, then placebo, during two contiguous study periods. The protocol will examine the effects of estrogen treatment on the fractional catabolic rate of very small high-density lipoproteins (HDL). Changes in very small HDL vs. typical HDL will be compared to changes in activity of hepatic lipase and to lipoprotein information. Also, the study will measure glucose and insulin metabolism and abdominal fat by MRI.